The goal of this project is to characterize and implement the unique properties of multiphoton excited fluorescence and nonlinear scattering for in vivo detection of cancer and novel in vivo studies in cancer biology. An engineering goal of this proposal is to construct a fully functional laser-scanning multiphoton endoscope capable of producing images of living tissue using primarily intrinsic fluorophores and collagen second harmonic signals that are of the resolution and quality currently obtainable;with a state-of-the-art multiphoton microscope. To accommodate the breath of this multidisciplinary proposal, there are three laboratories and a biomedical instrument company (Optiscan Imaging Ltd) involved, whose combined expertise encompasses all of the science and technologies required to successfully complete the project. The project leadership is centered at the NIH/NIBIB Developmental Resource for Biophysical Imaging and Opto-electronics (DRBIO) at Cornell University in the department of Applied and Engineering Physics. The three specific aims are: 1) A direct comparison of multiphoton imaging and spectroscopic parameters of intrinsic tissue signals with standard histological techniques, focusing on the discovery of new diagnostic criteria for cancer. 2) Construction of a raster-scanning fiber endoscope for multiphoton emission imaging in tissue. 3) Optimization of multiphoton microscopy for imaging mouse models of cancer, and an exploration of the potential of large field-of-view (~ 1cm2) multiphoton imaging as a diagnostic tool for clinical use. The overall goal of this program is to develop a new and powerful infrastructure for noninvasive, microscopic medical detection and diagnosis of premalignancy and cancer. We anticipate that methods established will be of general value for characterizing of carcinogenesis in other cancer models, and ultimately in human clinical applications.